I'm gonna assume you speak Spanish and don't understand how to read the website...
To download...
https://download3.nexon.net/Game/Comb...nloaderV65.exe
or
https://download3.nexon.net/Game/Comb...msSetupV65.exe
To register, just go to Combat Arms - Online FPS Action and hit the big, red play button. It will ask you to login but click on the "Click here to get started." link and it'll take you to the registration screen.